The conventional anchoring system was based on the idea of keeping a floating structure in position by means of anchoring lines, which included a chain cable with an anchor at its end, driven into the sea bed so as to be able to support horizontal loads. A set of 8 to 16 anchoring lines were deployed in series from the superstructure of the platform to the sea bed.
With the development of technologies for deep water oil recovery, it is becoming increasingly important to reduce the weight of the anchoring system on the deck of the platform and to reduce the amount of space occupied on the sea bed by the said anchoring system. As a result of these requirements, the so-called "taut-leg" system therefore came into being.
In this "taut-leg" system, a fixed point on the sea bed is needed, to which point the anchoring line for supporting vertical loads will be fastened, and use is made of elastic lines instead of a catenary of inextensible chain cables.
A number of devices have been suggested as the fixed point on the sea bed, the most commonly used by specialists in the field being piles and anchors.
Piles are fastened to the sea bed by driving or by drilling with a bore. Both technologies are sufficiently well known to the expert in the art.
Anchors may be classified into two main categories: suction anchors and vertical-load anchors.
Suction anchors comprise devices which are reminiscent of the shape of an inverted cup, which buries itself in the sea bed as a vacuum is formed inside it.
Vertical-load anchors (VLAs) generally consist of a flat sheet in various formats, these being driven into the sea bed by means of dragging, exerted on their mooring cable, until they reach the ideal position for supporting the vertical loads which will be required of them.
a pointed front part of the anchor; PA1 a cut-out in the portion corresponding to the tail of the anchor to allow fitting of a device used to launch the anchor; PA1 two longitudinally hollowed-out lugs mutually parallel extending perpendicularly from the upper face of the central portion of the flat sheet, and to which the mooring cables of the anchor will be attached; PA1 on the lower face of the central portion, two longitudinal bars extending perpendicular to the plane of the face, and convergent at an acute angle towards the front part of the anchor; PA1 two vertical slots provided at the upper ends of the said lugs, nearer to the tail than to the front part of the anchor, in which shackles for fastening the mooring cables of the tail of the anchor will be accommodated; PA1 two longitudinal slots which extend from the central portion of said lugs as far as the lower ends thereof, for receiving the shackles for mooring the cables of the anchor front part; and PA1 shearable pins in said longitudinal slots for limiting the travel of said shackles. PA1 a) taking the assembly formed by said launching device connected to said anchor on board a first vessel to the launching location; PA1 b) passing an anchoring line of the anchor to a second vessel located close to the launching location, the launching device having a support cable which is kept attached to the first vessel; PA1 c) lowering the said assembly, attached to its respective cables, down to a level spaced above the sea bed and releasing the support cable of the launching device to allow the assembly to drop under gravity and to penetrate the sea bed; PA1 d) recovering the launching device of the anchor and bringing it on board the said first vessel; PA1 e) dragging the said anchoring line of the anchor with the aid of the second vessel until the face of the anchor adopts a position which is perpendicular to the anchoring line, guaranteeing the grip necessary for anchoring the movable structure; PA1 f) attaching the end of the anchoring line to a marker buoy for holding it until the movable structure arrives at the location; and PA1 g) recovering the anchoring line with the aid of the buoy and of a vessel and connecting said anchoring line to the hawsers of the said movable structure, and releasing the marker buoy.
A second aspect of the invention comprises a process for deploying the anchor of the first aspect using a launching device, characterized in that it comprises the steps of:
The body of the pile is filled with a heavy material, for example cast iron, haematite, concrete, etc.